Fix React warning about state update of unmounted component

[gamtiq]

Hello,

I encountered the following React's warning when running unit tests for a component that is wrapping react-truncate:

Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in the componentWillUnmount method.

I researched and found that the problem is related to non-canceled requestAnimationFrame callback which asynchronously calls a function specified in onTruncate prop.
The proposed change eliminates the warning.